In the prior art heaters are commonly used in an enclosed area or container to control only the temperature of a given object or device by controlling the temperature around it or by controlling the surface or case temperature of an object or device. Thus, prior art heaters typically are inserted in an enclosure or box along with the device to be temperature maintained. If the box is subjected not only to environmentally low temperatures but additionally to environmentally high temperatures where the electronics in the enclosure could overheat, a heat sink needs to be added to dissipate the heat from the electronics package under the high temperature conditions of the environment. When a heat sink is added to the package or electronics module being heated or cooled, it is much more efficient at dissipating heat therefrom under the environmentally cold conditions and thus, it is harder to maintain the module at a "safe" temperature under these conditions. Therefore, a much larger heater needs to be installed in such a container when the enclosure is subjected to both very high and low temperature conditions. The additional heat requirements of such a situation not only greatly tax a power source but can, in some instances, provide so much heat wherein the environment is very cold that electronic components immediately adjacent the heater may be damaged.
The present invention attempts to overcome the above disadvantages by inserting a heater between the package to be heated and the heat sink so as to prevent heat transfer therebetween on the thermo-dynamics principle that heat is never transferred from a cool object (electronics package) to a higher temperature object (heating element). Thus, as long as the heating element is heated to a temperature just slightly higher than the temperature of the electronics module, no heat will be dissipated from the electronics module to the outside environment through the heat sink so matter how cold the outside environment is. Since no heat is being drained off the electronics module, the module can, in most cases, maintain a desired temperature in the closed container due to its own power dissipation therein. The heater will, of course, supply some heat to the electronics module to help keep the internal temperature in the container at the desired value. It is realized that heat will be dissipated from the heater to the heat dissipating surface of the cooling fins but it has been found that this heat dissipation is minimal as compared to the amount of heat dissipation occurring (and power required) if the heater were not interspersed between the electronic module and the cooling fins.
It is therefore an object of the present invention to provide an improved and more power efficient method of maintaining the temperature of an electronics module contained in an environmentally protective enclosure under cold extremes while not interfering with the dissipation of heat from the electronics module under environmentally high temperature extremes.